1. Field of the Invention
The present invention relates to a battery pack and a charging method for the same, and more particularly, to a battery pack and charging method for the same that regulate the full-charge voltage of a battery according to deterioration in lifespan of the battery.
2. Description of the Related Art
In a battery pack employing lithium-ion cells or lithium polymer cells, a safety circuit is electrically connected to a battery including an electrode assembly and electrolyte in a case. The battery is charged with and discharges electricity through chemical reactions, and the safety circuit prevents overcharge and overdischarge of the battery by regulating the charge-discharge process to protect the battery.
A full-charge mode is provided to the safety circuit to prevent overcharge. At the full-charge mode, when the charge voltage of the battery reaches a preset value, the safety circuit automatically terminates charging of the battery. Thus, the battery is prevented from overcharge and overheat and has a prolonged lifespan.
However, although the safety circuit prevents the overcharge, the battery inevitably suffers from with deterioration in lifespan such that capacity of the battery is lower than the initial capacity as time goes by.
Since a battery cell with deteriorated lifespan has a capacity lower than the initial capacity, the battery cell is overheated in a case of charging the battery cell up to a preset full-charge voltage preventing the overcharge. In a case of a battery cell repeatedly overheated, the deterioration of lifespan is accelerated when the battery cell is charged up to the initially set full-charge voltage so that the lifespan of the battery cell is shortened. Namely, the battery cell with deteriorated lifespan deteriorates stability of a battery pack.
In a portable electronic product such as laptop computer using a plurality of battery cells, the battery cells are charged at once. However, when any one of the battery cells has a deteriorated lifespan, there occurs cell imbalance. In other words, when there is a battery cell with deteriorated lifespan among the battery cells, since the deteriorated battery cell is charged with the initially set full-charge voltage, the lifespan deterioration is accelerated to shorten lifespan of overall battery cells.
When, in order to overcome the above-mentioned drawback, the full-charge voltage of a battery pack is set too low, since charging efficiency of the battery cells is inferior, power supply capacity of the battery pack is also inferior.